timmynz

Hi there,

New to biking and therefore to maintaining them but keen to learn. I have a Trek 2020 Marlin 7 29Inches MTB.

I have just replaced the chain as i snapped the old one twice. I have taken it out for a test but am having an issue when changing gear to the front big ring. The chain ends up wrapping around the front ring (see attached image) It happens about 10% of the time. I have tried adjust the front derailer but the problem still exists. Is the chain the right length?

Would appreciate and suggestions. I am keen to learn to maintain it myself.

Many thanks!

JoeTBM 

Snapping a chain is pretty hard to do. I am suspecting something else may have damaged the chain or drive chain. You say this is a 2020 model, so it's not like it has been abused for a long time and I would have guess you purchased it new.

Are you sure you have the proper chain for the number of speeds you have on the rear cassette.

For the chain to wrap like that I would suspect a bent tooth on the crank's chainring or a bent link causing the chain to fail leaving the chainring, I don't see how a misadjusted front DER could cause that. Normally changing a chain would not require adjustment of the DERs as they should not have been altered in the process.

Have you ever damaged the drive chain by hitting something? Have you had your LBS look at it for a warranty issue?

timmynz

Thanks for your response.

Yes I am faily sure it is the right chain. It is a 9 speed bike and I bought a Shimano cn-HG93 which is 9 speed.

It's was new in April. I have had a look at the teeth and they don't look bent. They do look fairly bad I think for a bike that has only had about 15hrs riding. Most of it causal riding because of lockdown. Do they look bad enough to cause possible issues?


Think I will take it to the local bike shop.

cheers

dsbrantjr

Snapping chains suggests either trying to shift under heavy pedaling load, or that they were not closed correctly when installed. Did you use a master link or Shimano special joining pin (right ways) or did you partially push out a pin and push it back in (wrong way)? If not perhaps your shifting technique needs work, you need to ease off on pedal pressure while shifting, especially a front shift to a larger ring..

JoeTBM 

What prompted you to change the chain in the first place on a 3 month old bike with little ride time? Were you having other issues?

timmynz

It snapped twice and everything I have read suggests if it happens once then replace it. My chain also had some bad reviews of it happening to others so I thought a new one would be be a cheap simple upgrade.

trailangel

Chain not routed correctly thru rear derailleur cage. Chain is on wrong side of tab between the idler wheels. Look at pic.

Retro Grouch 

That's classic chain suck. The bottom run of the chain isn't releasing from the chainring. I suspect the chain having broken previously is all part of the problem. My bet is your big chainring has been damaged.

Since it's a new bike, I'd take it back to the seller. If I were trying to fix it myself, I'd either examine that big chainring hoping to find a tooth I could either straighten or smoothen or else buy a new chainring.

dabac

good catch.
...although that usually only lead to noise. And some embarrassment for whoever installed the chain when it’s discovered.
chain suck as in pic 1 I’ve only associated with (lots of) wear, and dirty/dry chain/chainrings.
Perhaps if the chain was routed incorrectly from the start, this has accelerated wear to the point that chain suck starts to happen.

timmynz

Nice spotting. Fixed that but the issue still happening. The front chain ring teeth look straight but look worn for the age. Will take it back.

cobba

Is it the same length as the old chain that you broke?